This invention related to an optical disc recording/reproducing method, an optical disc and an optical disc device.
Conventionally, optical recording media such as a disc-shaped optical recording medium and a card-shaped optical recording medium using an optical or magneto-optical signal recording/reproducing method have been developed and provided on the market. As such optical recording media, there have been known read-only memory type recording media such as a so-called compact disc (CD), so-called write-once type recording media which enable data writing once on the user side, and rewritable recording media which enable so-called overwrite such as a magneto-optical (MO) disc.
In an optical disc device for carrying out writing/reading of data onto/from a disc-shaped recording medium, a laser diode for emitting a light beam for information recording/reproduction and a photodetector for detecting a reflected light of a light beam radiated onto an optical disc are provided. Using an optical head on which focusing servo and tracking servo are performed on the basis of the detection output from the photodetector, speed servo is performed on a spindle motor and the optical disc is rotated at a constant angular velocity or a constant linear velocity while a recording track of the optical disc is scanned with a light beam, thereby carrying out data recording/reproduction.
In a magneto-optical disc system prescribed by the International Organization for Standardization (ISO), blocked codes are employed.
In the format of magneto-optical disc prescribed by the ISO, the direction of user data is equal to the direction of data on the disc as shown in FIG. 1. In an ECC block using blocked codes, the direction of correction codes is interleaved with respect to the direction of data on the disc in order to improve the capability of correcting burst errors. Also, in this format, data immediately after frame synchronization FS belong to separate identical correction codes, and the second data from frame synchronization FS belong to separate identical error correction codes. Similarly, data immediately before frame synchronization FS belong to separate identical error correction codes.
At the time of recording on the optical disc of such a format, when all the user data sent from the application side for one ECC block is written into a buffer memory 302 through an arbiter 301, as shown in FIG. 2A, an ECC processing section 303 starts error correction coding. After coding of all the data in one ECC block is completed, the coded data is sent from the buffer memory 302 to modulation means and channel encoding is started. Thus, channel-encoded data is recorded in the user data area on the disc.
At the time of reproduction, reproduction data obtained from the disc is channel-decoded by demodulation means. When all the data for one ECC block is written into the buffer memory 302 through the arbiter 301, as shown in FIG.2B, the ECC processing section 303 starts decoding. After decoding of all the data in one ECC block is completed, the user data is taken out from the buffer memory 302 and is sent to the application side.
As described above, in the magneto-optical disc system prescribed by the ISO, the direction of user data is equal to the direction of data on the disc, and the direction of error correction codes is interleaved with respect to the direction of data on the disc. Therefore, at the time of recording, error correction coding cannot be started unless all the user data for one block is written into the buffer memory. Unless coding of all the data in the block is completed, channel encoding of coded data cannot be started and hence channel-encoded data cannot be recorded onto the disc. At the time of reproduction, decoding cannot be started unless reproduction and channel decoding of all the reproduction data for one block are completed. Unless decoding of all the data in the block is completed, the user data cannot be taken out from the buffer memory. Thus, the latency time therefor is a fixed delay at the time of recording/reproduction. As the ECC block size increases, the fixed delay increases in proportion to the block size.
In the case where special recording/reproduction is carried out such as after-recording for reproducing, processing and then recording data during a short period of time by effectively utilizing the random accessibility as a feature of the optical disc, it is desired that the fixed delay at the time of recording/reproduction is as short as possible.
In the case of special recording/reproduction such as after-recording, it is necessary to have a buffer memory corresponding to the time required for data processing between reproduction operation and recording operation and for access on the disc, in order to carry out continuous reproduction operation at a high speed, data processing and then continuous recording operation for securing a transfer rate. Also, not only a transfer rate which is approximately twice higher is required for carrying out reproduction and recording operation, but also the transfer rate needs to be higher for the time required for data processing and for access on the disc.
In the case of after-recording, it is considered that data may be recorded at a position on the disc from where it is reproduced. In the case of continuous reproduction and recording, too, the recording position is close to the reproduction position. Therefore, only a short access time is required and the data processing time may be problematical. In general, a frame synchronizing signal FS is provided at the header part of a frame. If bit slip is generated, re-synchronization can be carried out by using the frame synchronizing signal FS. If bit slip is generated at a halfway point of a frame, the timing is shifted in the portion following that point and demodulation cannot be carried out accurately, or the position of demodulated data is shifted. As a result, a data error is generated. After that, when a frame synchronizing signal FS is detected at the header part of the next frame, the correct timing is obtained and the data is accurately reproduced. That is, the data immediately after the frame synchronizing signal FS is more resistant to an error caused by bit slip, in comparison with the data immediately before the frame synchronizing signal FS.
Meanwhile, there has been recently a remarkable increase in the capacity of the ROM (read only memory) disc and the RAM (random access memory) disc using optical recording. Shortening of the wavelength of a semiconductor laser used for the optical head of the optical disc recording/reproducing device and increase in the numerical aperture (NA) of an objective lens for condensing a light beam onto the information recording surface of the optical disc are realized.
Reduction in the spot size is known as a technique for realizing a high-density phase-change type optical disc having a capacity greater than that of a DVD-RAM. The spot size on the recording medium is substantially provided by xcex/NA, and can be reduced by a technique using a short-wavelength semiconductor laser light source made of GaN or ZnSe or a technique of increasing the NA of the objective lens by a two-group lens represented by a solid immersion lens (SIL).
For example, on the assumption of xcex=640 nm and NA=0.85, the diameter of the spot is approximately 0.75 xcexcm on the medium. If signals are recorded/reproduced by using RLL(1, 7) modulation, a linear recording density of approximately 0.21 xcexcm/bit can be realized.
As typical modulation codes of a modulation system having a broad detection window of the channel suitable for high-density recording/reproduction, an RLL(1, 7) code and an (2, 7) code are known.
RLL(1, 7) modulation is a type of modulation with a run length limited (RLL) code having a maximum inversion interval of waveform string, in which the minimum run of information (symbol) 0 is 1 and the maximum run is 7.
In RLL (1, 7) modulation, when converting data having a basic data length of m bits to a variable-length code (d, k; m, n; r), for example, data having a basic data length m equal to 2 bits is converted to a variable-length code (1, 7; 2, 3; 2) having a minimum run d of 0 equal to 1 bit, a maximum run k of 0 equal to 7 bits, a basic data length m equal to 2 bits, a basic code length n equal to 3 bits and a maximum constraint length r equal to 2 bits, by using a conversion table including a code for restraining continuation of the minimum length d of 0 of the channel bit string of the RLL(1, 7) code for a predetermined number of times. For this RLL(1, 7) modulation, the following conversion table is used.
In this RLL(1, 7) modulation, if the bit interval of the recording waveform string is T, the minimum inversion interval Tmin is equal to 2T. If the bit interval of the data string is Tdata, The minimum inversion interval Tmin is equal to 1.33(=(m/n)xc3x97Tmin =(⅔)xc3x972) Tdata. The maximum inversion interval Tmax is equal to 8(=7+1)T(=(m/n)xc3x97Tdata=(⅔)xc3x978Tdata=5.33Tdata. The detection window Tw is equal to 0.67(=⅔) Tdata On the other hand, in RLL(2, 7) modulation, when converting data having a basic data length of m bits to a variable-length code (d, k; m, n; r), for example, data having a basic data length m qual to 2 bits is converted to a variable-length code (2, 7; 1, 3; 2 ) having a minimum run d of 0 equal to 2 bits, a maximum run k of 0 equal to 7 bits, a basic data length m equal to 1 bit, a basic code length n equal to 3 bits and a maximum constraint length r equal to 2 bits, by using a conversion table including a code for restraining continuation of the minimum length d of 0 of the channel bit string of the RLL(2, 7) code for a predetermined number of times. For this RLL(2, 7) modulation, the following conversion table is used.
In this RLL(2, 7) modulation, if the bit interval of the recording waveform string is T, the minimum inversion interval Tmin (=(d+1)T) is equal to 3T. If the bit interval of the data string is Tdata, the minimum inversion interval Tmin is equal to 1.5(=(m/n)xc3x97Tminxc3x97(xc2xd)xc3x973) Tdata. The maximum inversion interval Tmax (=(k+1)T) is equal to 8(=7+1)T(=(m/n)xc3x97Tmax)Tdata=(xc2xd)xc3x978Tdata=4.0Tdata. The detection window Tw (=(m/n)xc3x97T) is equal to 0.5(=xc2xd)Tdata. In the optical disc system using an optical head having a high-NA objective lens, it is necessary to enhance the error correction capability in order to cope with errors due to the influence of dust particles or scratches on the optical disc surface onto the light beam. To enhance the error correction capability, codes are increased or the ECC block is increased. Moreover, there is proposed a method of interleaving and collectively blocking the error correction codes in order to broaden the ECC block to the size equivalent to one track on the inner circumference of the disc.
If blocked codes are used, a block size of not smaller than 64 KB can be constituted as user data even when general GF(28) is used as codes. In addition, the present Assignee has proposed, in the Japanese Publication of Unexamined Patent Application No. Hei 9-285899, an optical disc recording/reproducing method, an optical disc and an optical disc device in which address information is provided as a part of data within a frame so that a common data format is used for both a read-only disc and a recordable disc. According to this technique, in a block format determined as shown in FIG. 3, the code length of the ECC block is 196 (172 information words and 24 parity words), the interleave length is 384, the number of sectors in this block is 16, the number of frames per sector is 49, the number of data within a frame is 96, and the user data per sector is equivalent to 4 KB. The data of 24 bytes within the leading frame of each sector is address information. The direction of data on the disc corresponds to frames 0, 1, 2 , . . . , 783 (blocks=total sectors).
In the block format shown in FIG. 3, the interleave length is long in comparison with the frame length, and the header data of each frame is not on the same code but is concentrated at one of the four codes.
It is an object of the present invention to provide an optical disc recording/reproducing method, an optical disc and an optical disc device for recording/reproduction of data in a disc format such that the fixed delay at the time of recording/reproduction can be reduced.
It is another object of the present invention to provide an optical disc recording/reproducing method, an optical disc and an optical disc device for recording/reproduction of data in a disc format such that correction incapability caused by concentration of data of a specified position within a frame to a specified code can be avoided.
In the case of reproduction, the correction capability with respect to a product code (PRC) can be improved by strategy. However, this can be realized on the assumption that correction processing is carried out for a plurality of times.
On the other hand, in the ECC block formed by interleaving and collectively blocking error correction codes so as to broaden the ECC block to the size corresponding to one track on the inner circumference of the disc for improving the error correction capability, the code structure is in one direction and therefore the number of times of correction is basically one.
At the time of recording, too, the product code must be encoded in two directions, that is, parity generation must be carried out. However, if blocked codes are used, encoding is carried out only in one direction.
Thus, if the block size of the ECC block is the same, the fixed delay at the time of recording/reproduction is smaller for the ECC block using blocked codes which require a smaller number of times of correction, than in the case where the product code is used.
Moreover, the fixed delay at the time of recording/reproduction can be significantly reduced by causing the direction of user data (input/output order) to be equal to the direction of correction codes as shown in FIG. 4. In the case of FIG. 4, the direction of correction codes and the direction of user data are made coincident with each other, using the same capacity as that of the magneto-optical disc prescribed by the ISO.
In the optical disc system having such a disc format that the direction of correction codes and the direction of user data are made coincident with each other, in reproduction, correction operation for reproduction data is carried out from when transmission of data for one ECC block from the demodulator is completed. This is because the direction of correction codes is interleaved with respect to the direction of data on the disc. Then, the user data can be transmitted to the buffer memory from when correction of one code is completed. That is, it is not necessary to wait for correction operation for one ECC block. This is because the direction of correction codes and the direction of user data are made equal to each other.
Similarly, in recording, coding can be started at the time when necessary data for generating one code is transmitted, without waiting for user data for one ECC block from the buffer memory. After that, when coding of one ECC block is completed, the data is transmitted to the modulator and recorded onto the disc.
The operation timing in this optical disc system is shown in FIG. 5, in comparison with the above-described case of the magneto-optical disc system. As shown in FIG. 5, the fixed delay at the time of recording/reproduction can be reduced by the amount of xe2x80x9cmarginxe2x80x9d in reproduction and recording. Also, a margin can be provided for data processing in reproduction and recording. Alternatively, the total data processing time and therefore the buffer memory can be reduced. In addition, since the direction of correction codes is the same as the direction of user data, no memory for data rearrangement is required and the hardware structure can be minimized. Also, since less data transmission/reception takes place between the buffer memory and the external device, bus arbitration can be easily carried out.
Moreover, higher resistance to errors can be obtained by dispersing words within the same code to a broad range of words within the frame.
According to the present invention, data recording/reproduction is carried out, for example, in a format such that interleave processing is performed on error correction codes so as to collectively block the error correction codes into an error correction unit and that the input/output order of user data in an ECC block as an error correction unit is made coincident with the direction of processing of the error correction codes.
Also, according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the ECC block is constituted by one or more sectors, the sector is constituted by a plurality of frames, the block length of the ECC block is expressed by the following equation,
block length=number of sectorsxc3x97number of framesxc3x97frame length=code lengthxc3x97interleave length
the number of sub-sectors is expressed by the following equation,
number of sub-sectors=number of sectorsxc3x97p
(where p=number of segments: natural number) and {code lengthxc3x97interleave length}/{segment lengthxc3x97number of sub-sectors} % number of sub-sectors (where % indicates modulo) and the number of sub-sectors are prime numbers, respectively.
Also, according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the ECC block is constituted by one or more sectors, the sector is constituted by a plurality of frames, the block length of the ECC block is expressed by the following equation,
block length=number of sectorsxc3x97number of framesxc3x97frame length=code lengthxc3x97interleave length
the number of sub-sectors is expressed by the following equation,
number of sub-sectors=number of sectorsxc3x97p
(where p=number of segments: natural number)
and when the code length is divisible by q (where q=number of subblocks: natural number), {{code length/q}xc3x97interleave length}/{segment lengthxc3x97number of sub-sectors} % number of sub-sectors (where % indicates modulo) and the number of sub-sectors are prime numbers, respectively.
Moreover, according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the number of data within the segment is smaller than the number of data within the frame and that the correction code position is updated for each segment while the interleave rule is met in causing the data position on the disc to correspond to the data position on the ECC block.
Also, according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the correction code position is updated by one byte.
Also, in the optical disc recording/reproducing method and the optical disc device according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the ECC block is constituted by one or more sectors, the sector is constituted by a plurality of frames, the block length of the ECC block is expressed by the following equation,
block length=number of sectorsxc3x97number of framesxc3x97frame length=code lengthxc3x97interleave length
and a sector ID is provided holding the following relations.
sector ID lengthxc3x97number of sectors interleave lengthxc3x97k
(where k is a natural number)
sector ID length=segment lengthxc3x97p
(where p=number of segments: natural number)
Also, in the optical disc recording/reproducing method and the optical disc device according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that {code lengthxc3x97interleave length}/{segment lengthxc3x97number of sectors} % number of sectors (where % indicates modulo) and the number of sectors are prime numbers, respectively.
In addition, according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the number of sectors is 2n and that {code lengthxc3x97interleave length}/{sector ID lengthxc3x97number of sectors} is an odd number.
Also, in the optical disc recording/reproducing method and the optical disc device according to the present invention, data recording/reproduction is carried out, for example, in a disc format such that the number of data within the segment is smaller than the number of data within the frame and that the correction code position is updated for each segment while the interleave rule is met in causing the data position on the disc to correspond to the data position on the ECC block.
Moreover, according to the present invention, data recording/reproduction is carried out, for example, in a plurality of disc formats having different ECC block sizes in accordance with the setting of the number of sectors and interleave length.